Jeez, I had a long post for you and lost it! Instead of trying to redo it, I will just say it is too early for planting outside any plant in zone 6. I am giving you a link to MU's extension website. It is a wealth of information for growing anything in the state of Missouri. I don't know what state you are in, but there should be a similar website for most states.

Here is a link that might be useful: Horticulture

Zinnias are a good choice for a sunny area but it's too early as gldno said. They are easy to grow from seed.
Other annuals that would give you lots of color are annual vinca for a sunny area or impatiens for shade. They'll be selling those in flats at Wal-Mart and Lowe's soon but wait until late April or the frost may get them. They're usually inexpensive and easier to buy in flats instead of trying to grow from seed - for me anyway. Planting several of one color will make more of an impact from a distance than alternating colors. Personal choice though. My neighbor had a huge drift of white vinca in front of their dark colored house one year that was very showy.

Zinnias are great! Some newbie tips for this flower.

1. Watch out for rabbits & aphids when they start coming up. I like to plant my seeds then throw light chickenwire over the area to keep the rabbits off of them. They grow up through the chicken wire and cover it up & protect themselves when they're little. As far as aphids, I use aphid killer in a spray bottle from the store. If you get Japanese beetles, bug in a bag works well from what I hear.

2. After they get big and blooming, they might start to get mildew. Mix up some baking soda & water in a spray bottle & mist them down.

3. Zinnias love sun & are gorgeous. You might try your hand at cosmos seeds, they are one of the most low maintenance plants with unbelievable color & bloom. Sun lovers as well.

Finally, go over to the wintersowing forum. I just started it this year & I'm crazy for it. It will give you the chance to start gardening now & planting when others are just starting to throw down seeds.

Yeah! Now's the time to winter-sow those warm sunlovers! You really should check out the winter-sowing forum if you have an itch for zinnias and other warm weather plants...

Thanks guys, for the info. Gonna check out winter sowing.

I like the ruffles hybrid zinnias. You have to order the seeds, but I think they are worth it. If you haven't done much gardening, try getting a big pretty plastic pot. There are some nice ones at Lowes for about $25. and fill it with a soilless mix not cheap potting soil. It will cost around $8.00 for 2 cubic feet. You won't have to water as much if you get a really big pot. You can have a little garden in a big pot.

I'm new to Missouri but not to gardening .... I just wanted to add you could plant some shrubs now...spirea's etc. March is also a good time for zone #6 tree plantings or transplanting. Like everyone said the annual garden should wait. Last year though; I did plant my window boxes and planters the first part of April..so the wait isn't long now!!! Also phlox can go in now and of course the good ole pansies! I'd ask at my local garden center for advice as well.

Happy Gardening!!